(a) Field of the Invention
This invention relates to a method for preparing 2-phenylbenzotriazoles having the following general formula I, which are useful as an ultraviolet ray absorber.
This invention further relates to a method for preparing 2-phenylbenzotriazole-N-oxides having the following general formula II, which are a useful intermediate for said 2-phenylbenzotriazoles.
(b) Description of the Prior Art
2-phenylbenzotriazoles having the following general formula I, ##STR4## (wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group having a carbon number of 1 to 4, a lower alkoxyl group having a carbon number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 represents hydrogen or chlorine atom, a lower alkyl group having a carbon number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 1 to 4, phenyl group, a phenyl group substituted with an alkyl group having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl part of which has a carbon number of 1 to 4) are known to be useful as an ultraviolet ray absorber to be added to plastics, paints, oils and the like.
2-phenylbenzotriazole-N-oxides having the general formula II, ##STR5## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as defined above with regard to the general formula I) are known to be an important intermediate for said 2-phenylbenzotriazoles.
Heretofore, these 2-phenylbenzotriazoles and 2-phenylbenzotriazole-N-oxides have been produced by chemically or electrolytically reducing o-nitroazobenzene derivatives having the general formula III, ##STR6## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as defined above with regard to the general formula I). However, these conventional methods respectively have merits and demerits, and are not always satisfactory.
For example, Japanese Patent Publication No. 37-5934 and U.S. Pat. No. 3,773,751 disclose a method for preparing 2-phenylbenzotriazoles or 2-phenylbenzotriazole-N-oxides by chemically reducing o-nitroazobenzene derivatives in an alcoholic sodium hydroxide solution with zinc powder at a satisfactory yield. However, this sodium hydroxide-zinc system produces zinc sludge which results in waste water contamination problems.
As disclosed in U.S. Pat. No. 2,362,988, ammonium sulfide, alkali-sulfide, zinc-ammonia system, hydrogen sulfide-sodium system and zinc-hydrochloric acid system are used as a chemical reducing agent for the above mentioned reduction reaction. However, this conventional method produces a large amount of sulfite or zinc salts which result in waste water contamination. The sulfite further generates sulfurous acid gas, and the used sulfide type reducing agent generates poisonous hydrogen sulfide, which results in environmental polution problems.
Japanese Patent Laid Open Nos. 51-138679 and 51-138680 disclose a reduction method by the addition of pressurized hydrogen. Japanese Patent Laid Open No. 50-88072 discloses a reduction method by hydrazine. However, these methods are not satisfactory in view of yield and economy, and it is impossible to obtain the desired product of high purity because a side reaction is caused during the main reaction. Particularly, in the case of producing a chlorine-containing product, a side reaction such as dechlorination reaction is caused.